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Thread: M7100 Ignition Sense Voltage Spike Issue & Fix

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    Exclamation M7100 Ignition Sense Voltage Spike Issue & Fix

    This issue came up in another venue, and I thought I would post it elsewhere for everyone’s benefit…


    I STRONGLY suggest putting a noise filter in the ignition sense (yellow) wire on any M7100 radio. Back in the mid-2000's there was an issue with the M7100's with a short NEGATIVE voltage spike (>100 V) occurred in some vehicles, when the vehicle was started, destroying the MOSFET ignition sense device in the M7100's. The usual symptom observed by the user is the radio will not turn-off. See Image.

    NEGATIVE IGNITION VOLTAGE SPIKE.jpg



    BACKGROUND:
    In the Orion radios, this switching function was handled by an [analog] relay (K601), which was "upgraded" to a solid-state device in the M7100's.


    First observed in February 2008, the spike was only detectable on a storage Oscilloscope. Too fast for the VOM, DVM, VTVM to detect. The preventative fix was to place an inexpensive 5 Amp (or less) DC Noise Filter in the [Yellow Wire] Ignition Sense circuit. This recommendation was implemented in the M7100’s Installation Manual [MM102342V1], and an extract of this page is attached below as a PDF.

    For radios already damaged, replacement of the Mosfet is the only remedy. I have the repair instructions if anyone needs them.


    Ignition Sense Voltage Spike Issue - extract.pdf
    Gatorbait3014
    Retired Master Two-Way Radio Master Technician & System Engineer (34+ years)

    My goal in life is to become as wonderful as my dog thinks I am.



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    MotFAN (Jun 13, 2018),motorola_otaku (Jun 13, 2018)

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    Now you tell me. I replaced the M7100 with an M7300 after I replaced the mosfet twice.
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    Not something I've observed in my M7100 installs, but thanks for the heads-up. Is it only an issue in dashmount, single radio installs? All of mine were remote dual radio setups.
    "The Girl Scouts found several hungry REACT members at the finish line..."

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    What kind of vehicle was this. This problem could affect other equipment as well.

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    Rather than replying individually, I will do it all at once...

    COM501: It is printed in the installation manuals, but it popped-up in another forum, and felt it wise to post in all the GE/Harris radio forums, given users might not be using installation manuals new enough to contain the information....If they even use a manual.

    motorola_otaku: The YELLOW Ignition Sense wire, regardless of under-dash or remote mount, eventually feeds back to the vulnerable Mosfet circuit, which is located in the main body of the radio (aka: the drawer unit).


    RFI-EMI-GUY: Initially seen in School Buses, but later seen in all flavors of vehicles, including sedans.

    (The School Buses were the first vehicles to be installed onto the new system. They were intended to be the coverage "Guinea Pigs", as School Buses usually go everywhere! For that very reason, School Buses and Garbage Trucks are traditionally the best user group to utilize for final coverage testing on a live system, prior to migrating public safety users.)
    Gatorbait3014
    Retired Master Two-Way Radio Master Technician & System Engineer (34+ years)

    My goal in life is to become as wonderful as my dog thinks I am.